As technology progresses, people receive more information from electronic devices, such as multimedia players, network communication devices, and computers, which are equipped with display devices such as CRTs or LCDs for displaying images. The number of pixels and size of the image displayed by the display devices are constrained by the size of the display devices and their performance. Hence, the conventional CRT or LCD displays cannot meet the requirement of compact, portability, and a size with high display quality. For resolving this problem, the head-mounted display (HMD) is provided in the market. The head-mounted display provides one or two small tubes or LCDs disposed in front of the left and right eyes of a person. For example, a head-mounted display achieves stereoscopic effects by using binocular parallax, which projects images outputted from the tubes or LCDs through beam splitters onto the eyes of the user.